The current main stream of the production of L-amino acids such as L-glutamic acid is the fermentative production utilizing coryneform bacteria. As for the fermentative production of L-amino acids, it has been attempted to reduce the cost based on breeding of strains with superior productivity and development of fermentation techniques. Although conventional attempts for realizing the cost reduction were mainly directed to achieving higher yield, energy required for cooling the fermentation heat generated during the culture cannot be ignored in addition to the raw material as the factors concerning the fermentation cost. That is, as for usual microorganisms used for the fermentation, the temperature of the medium rises due to fermentation heat generated by the microorganism themselves during the fermentation, and hence enzymes required for the fermentation may be inactivated or the productive bacteria may be killed. Therefore, it is necessary to cool the medium during the fermentation. Accordingly, in order to reduce the cooling cost, fermentation at high temperatures has been studied for many years. Moreover, if high temperature fermentation becomes possible, the reaction rate may also be improved. However, as for the L-amino acid fermentation, effective high temperature culture has not been realized so far.
Corynebacterium thermoaminogenes is a bacterium classified into coryneform bacteria like Corynebacterium glutamicum (Brevibacterium lactofermentum), which is commonly used for the fermentation of L-amino acids. However, it shows the optimum growth temperature of 37–43° C., which is higher than that of Corynebacterium glutamicum, i.e., 30–35° C., and shows the optimum temperature for L-glutamic acid production of 42–45° C., which is considerably shifted to the high temperature region (Japanese Patent Laid-open (Kokai) No. 63-240779/1988).
Meanwhile, there have been developed techniques for enhancing L-amino acid producing ability of Corynebacterium and Brevibacterium bacteria by introducing a gene coding for an L-amino acid synthesis system enzyme derived from Escherichia coli or Corynebacterium glutamicum into them. Examples of such an enzyme include, for example, citrate synthase (Japanese Patent Publication (Kokoku) No. 7-121228/1995), which is an enzyme of the L-glutamic acid biosynthetic pathway, glutamate dehydrogenase (Japanese Patent Laid-open No. 61-268185/1986), isocitrate dehydrogenase, aconitate hydratase (Japanese Patent Laid-open No. 63-214189) and so forth.
However, any L-amino acid biosynthesis enzymes and genes coding for them derived from thermophilic coryneform bacteria have not been reported.